High pressure common rail fuel pumps for different engines have a variety of different characteristics suitable for their specific applications. Often times development of a new engine and associated fuel system can require a new pump design. Those skilled in the art will appreciate that designing, developing, testing, etc. a new pump can involve considerable expense. While this expense may be distributed over the expected number of engines, when volumes are relatively low, the per engine development cost can be relatively high. Unfortunately, there has often been no alternative since an off-the-shelf alternative is typically unable to meet, or be easily modified to meet, all of the specific requirements of the new fuel system application.
High pressure common rail pumps are typically driven via a rotating shaft coupled to the engine crank shaft via a gear train. Depending on the specific pump design, torque reversals can occur typically after a pumping stroke has concluded. Torque reversals are sometimes the result of the pumping chambers inherently having greater than zero volume at top dead center in conjunction with a cam lobe backside profile that allows the stored energy in the pressurized fuel remaining in the pumping chamber to push in a reverse direction on the cam shaft immediately after passing through top dead center. These torque reversals can produce unwanted stress in the gear train and cam shaft, as well as produce undesirable noise emissions.
In most common rail fuel pumps, such as those illustrated for example in U.S. Pat. Nos. 5,701,873, 6,216,583 and 6,764,285, the pump pistons and cams are arranged in such a way that the cam shaft undergoes repeated bending loads with each pumping stroke. These repeated loads over the life of the pump can cause significant wear on bearings supporting the cam shaft. Because common rail fuel pumps often raise fuel pressure to extremely high levels, and are expected to undergo many millions of pumping strokes in their useful life, bearings can prematurely wear and the cam shaft can suffer from cyclic fatigue loading. These factors can cause the pump to be overdesigned to compensate for these cyclic stresses, or can result in premature failure of a pump if these stress issues are not adequately taken into account. In either case, costs are undesirably increased.
The present disclosure is directed to solving one or more of the problems set forth above.